1. Field of the Invention
The invention relates to a method and an apparatus for the manufacture of a tube made of film on a cellulose basis, which an insert reinforces, by extruding an aqueous solution of cellulose-N-methyl-morpholin-N-oxide (NMMO) onto the insert, which is drawn from a roll and formed to a tube with an overlapping longitudinal seam.
2. Description of Related Art
Cellulose is not soluble in common solvents and has neither a melting point nor a melting range and therefore cannot be worked as a thermoplastic. For this reason cellulose is normally converted chemically for the manufacture of casings for foods, such as sausage casings, this process involving a degradation of the cellulose, i.e., the average degree of fit polymerization of the cellulose is lower. Such methods are technically very complicated and accordingly expensive to practice.
Presently the viscose method is preferred in the extrusion of film tubes on a cellulose basis. The cellulose is reacted with caustic soda solution and then reacted with carbon disulfide. Thus, a cellulose xanthate solution is obtained, which is extruded through a spinning or ring nozzle into a so-called spin bath or coagulating bath. The cellulose is regenerated by means of additional coagulating baths and washing baths.
It has long been known that cellulose is soluble in oxides of tertiary amines, and that at present the most appropriate solvent for cellulose is N-methyl-morpholin-N-oxide (NMMO). The cellulose dissolves therein, without changing chemically. No breakdown of cellulose chains takes place. The preparation of appropriate spinning solutions is known (DD 218 104; DD 298 789; U.S. Pat. No. 4,145,532, U.S. Pat. No. 4,196,282, U.S. Pat. No. 4,255,300).
Filaments can be made from the solutions by extrusion into a spin bath (DE-A 44 09 609; U.S. Pat. No. 5,417,909). In WO 95/07811 (=CA 2,149,218) there is also disclosed a method for the preparation of cellulose tubular films by the aminoxide method. What is distinctive of this method is the cooling of the extruded film with a cooling gas immediately under the ring gap of the extrusion nozzle. According to EP A 662 283, the extruded tubular film is cooled from within by a liquid.
Recovery and purification of the NMMO are described in DD 274 435. Since the cellulose is not chemically converted in the process the apparatus cost is lower. In the aminoxide method no gaseous or aqueous waste products are produced, so that there are no problems with exhausts or waste water. It is therefore acquiring increasing importance.
In EP-A 0 686 712 the production of flexible cellulose fibers by the N-methylmorpholin-N-oxide-(NMMO) is described. In it a cellulose solution in aqueous NMMO is forced through a spinneret, carried across an air gap into an aqueous coagulating bath containing NMMO and then washed, finish-treated and dried.
According to WO 93/13670 a seamless, tubular food casing is made by extruding a solution of cellulose in NMMO/water by means of a special extrusion die. Between the extrusion die and the coagulating bath there is an air gap. Distinctive of this method is an especially formed hollow mandrel through which the coagulating liquid can circulate also inside of the tube. In the air gap the interior of the extruded tube is filled virtually completely with the hollow mandrel and the coagulating liquid. The tube is not stretched transversely.
In WO 95/35340 a method is described for the production of cellulose blowing films in which a non-derivatized cellulose dissolved in NMMO is used.
Document GB-A 1,042,182 describes a method for the production of a film tube on a cellulose basis reinforced by an insert by extruding a cellulose-NMMO solution onto the insert, the insert being drawn from a roll. The insert is formed into a tube with an overlapping longitudinal seam, the seam not being cemented. This tube is treated inside and out with a viscose solution.
Document DE-A 1 952 464 describes an apparatus for coating and imbibing a paper tube with polyvinyl alcohol resin. The paper tube is formed from a paper web. A cementing apparatus for cementing the overlapping longitudinal seam is not provided. Neither is any preheating of the paper web before it is coated with the polyvinyl alcohol resin performed.
In the document WO-A 95/07811 an apparatus is described for the production of tubes by extruding a cellulose-NMMO solution. The tubes are pure cellulose casings, but not so-called fiber casings in which a fiber insert strengthens the tube. The apparatus for the production of the tube is designed so that the tube can be cooled inside and out with air, so that the NMMO solution solidifies rapidly. The cooling air is by no means supporting air that is introduced into the interior of the film tube.
In the state of the art, methods and apparatus are known for the production of a fiber-reinforced cellulose tube by the viscose process, but these methods and apparatus are not applicable in NMMO technology for the following reasons:
Different temperatures of the spinning solutions
Different viscosities of the spinning solutions
Different solvents
Different sensitivities to evaporation and dilution, temperature fluctuations, and different temperature limits.
Usually the cellulose in the viscose process is spun in the temperature range of 20 to 45xc2x0 C. Instead, the extrusion temperature of cellulose NMMO solutions is around 85 to 115xc2x0 C.
The viscosity of cellulose in the viscose process is about 10 to 30 Pas, and that of NMMO solutions 10 to 300 Pas, especially 20 to 200 Pas. Cellulose in the viscose process reacts with caustic soda solution and then with carbon disulfide, while the NMMO solutions are organic solutions.
The invention is therefore addressed to the problem of designing a method and an apparatus so that they will be suitable for coating inserts formed into a tube with cellulose NMMO solutions and permit a uniform penetration of the inserts with cellulose-NMMO solutions.
This problem is solved by the invention in that the tube passes through a heating section situated ahead of the nozzle block and in communication therewith, in which the insert is preheated with hot air to the temperature of the extruded cellulose-NMMO solution, then the seam is cemented with straight NMMO or cellulose-NMMO solution and the tube is then carried through the nozzle block in which the cellulose-NMMO solution is applied to the tube and penetrates it to obtain an insert-reinforced film tube, that the interior of the film tube is filled with an aqueous NMMO solution, and that the film tube exits the nozzle block and enters a spin bath, is turned around in the latter, and is carried out of it.
In an embodiment of the process, after it is drawn from the roll, emulsifiers, wetting agents and/or anchoring agents are applied by one of the known methods such as roller application. An appropriately pressure-controlled supporting air is blown into the interior of the film tube after it leaves the nozzle block.
As the process continues, the film tube is carried through a heated annular gauging disk through which a heating medium flows in a controlled circuit.
In embodiment of the process, aqueous NMMO solution is delivered into the interior of the film tube and also removed therefrom, the delivery and removal being performed at a distance apart from one another. At the same time the level of delivery of the aqueous NMMO solution in the film tube is adjustable and its removal is performed such that the level in the film tube is variably up to 20 mm higher and up to 45 mm lower than the level in the spin bath.
The rest of the process is to be found in the features of claims 7 to 12.
As a variant of this process it is also possible, instead of passing through a tub filled with the spin bath, to apply the spin bath directly internally and externally onto the film tube, through ring nozzles for example, as is described in EP-A0 006 601. The spin bath level is then lowered inside and out to the top edge of the spin tub""s deflector roll.
The apparatus for producing a film tube on a cellulose basis, which the insert reinforces, by extruding an aqueous cellulose-N-methyl-morpholin-N-oxide-(NMMO) solution onto the insert, with a nozzle block and a spin bath, is characterized in that a supply roll for the insert, a deflector roll, and a forming section in which the insert is formed into a tube with an overlapping longitudinal seam, are present, that a preheating system for the tube is disposed ahead of the nozzle block, that the preheating system is connected by hot air ducts and an exhaust duct is connected with a controllable heater out of which air heated in the circuit flows into the preheating system, and from which cooled air flows back into the heater, and that the tube runs through the nozzle block which is preceded by a cementing system for cementing the longitudinal seam of the tube and which contains a ring nozzle out of the nozzle gap of which the cellulose-NMMO solution is applied to the tube preheated to the temperature of the extrusion solution in order to complete the formation of the film tube.
In further embodiment of the apparatus, the insert is selected from the group, paper, nonwoven, fiber fleece, fiber paper, the fibers being especially long hemp fibers.
In embodiment of the apparatus, after the insert is drawn from the supply roll an applicator system is attached, with which additives such as emulsifiers, wetting and/or anchoring agents can be applied to the insert and can be dried in the following hot open air section.
It is also possible that the preheating system is not required in every case, so that in certain manufacturing procedures it remains shut off.
In an embodiment of the invention, the nozzle block contains a ring nozzle which is heated by a heating medium, and a delivery tube and a removal tube for the aqueous NMMO solution, plus a duct for supporting air for the film tube, are brought centrally through an annular gauging disk which is arranged concentrically with the ring nozzle in the interior of the film tube and forms with the latter an annular gap through which the film tube passes.
The annular gauging disk is connected with the heating circuit for heating.
In embodiment of the apparatus, the infeed tube and the outfeed tube are adjustable for height within the film tube.
The further configuration of the apparatus will be apparent from the features of claims 19 to 25.
By the method of the invention a substantially uniform penetration of the insert with the cellulose-NMMO solution, so that, after passing through additional treatment steps, such as precipitation or coagulation baths, a composite of a fiber-reinforced film tube is obtained which has improved properties for its use. The fiber-reinforced film tube on a cellulose-NMMO basis corresponds in its properties to the known cellulose fiber or fiber casings which are made from cellulose hydrate and reinforced with wet-strengthened fibers of cellulose (=cellulose fiber fleece).